For me, I vote for Dante and I'll state my reasons clearly so I won't be attacked by "NERO HATER!" dudes and duddettes.
For me, that childish personality is exactly what attracted me to Dante. Especially in DMC 3 when he got attacked in the office. The jukebox is apparently vital if you're gonna fight a horde of demons xD. Also, Dante is like any other people with feelings except that he hides it better than most. Though his attitude in DMC 4 is not much different, but he just had this aura that made me less attracted. In a way, I guess I could say that his ****yness was put in a wrong way. It rocks, just the timing isn't right. But DMC 3 made up for that. A truly 'Dante Rulez' game, that 3.
Now let's take a look at Nero. Personally, I don't have anything against this guy. He kinda reminded me of Dante, only with less ****yness and more rebellious. Though his determination is something that should be admired. But seriously, no matter how you look at him, you can't help but dub him a 'Dante Clone'. Maybe it has to do with the hair being the same colour, heavy clothing, and attitude? If Nero was the main hero, then Dante would be a 'Nero Clone'. Twisted Logic FTW!
If Nero had his own 3 DMC series, it would've been hard to choose who. But since Dante has 3 main DMC games and Nero only 1, I go for Dante. Hooray for pizzas!!!